The harmful effects of asbestos exposure have been identified in numerous cohorts involved in the mining and fabrication of asbestos products. This proposal requests funds for a cohort and nested ease-control analysis of mortality among Sheet Metal Workers, members of the building trades with significant, intermittent asbestos exposure. Although several studies have described the effect of asbestos exposure on health of construction workers, the majority have been cross-sectional screening programs or analyses of proportionate mortality. These studies demonstrate the presence of asbestos related disease, but due to methodological limitations do not quantify levels of risk: The majority of data available on the risk of asbestos disease in construction comes from studies of insulators. However, insulators, faced exposures far higher than the majority of the building trades. Investigation of mortality in Sheet Metal Workers provides the opportunity to directly measure the risk of asbestos related disease in a cohort with intermittent asbestos exposure, secondary to their work in construction. A further, unique advantage of the proposed study is the opportunity to combine the analysis of mortality with the findings of a screening program for asbestos related disease. In 1986, Sheet Metal Workers who were members of this cohort were invited to participate in a nationwide medical screening program. Data on work history, job tasks, current symptoms, smoking histories and the results of pulmonary function tests - and chest x-rays are available for 12,454 union members. The existence of these data allows the exploration of hypotheses relating health status at the time of medical screening with subsequent mortality. A nested case-control study within the screened cohort is also proposed to examine the important question of whether radiographic signs of asbestos exposure, pleural and parenchymal changes, predict lung cancer mortality. To increase the quality of the x-ray data, a panel of three "B" readers will re-read all x-rays. Finally, comparison of cause specific mortality between the population participating in the screening program (respondents) with those who did not (non-respondents), will allow examination of participation bias. This ability to explore participation bias is rare in occupational cohort studies.